In order to determine if there are real differences in body size and shape between Indian-origin (IN) and Chinese-origin (CH) rhesus monkeys, we measured 833 rhesus monkeys during the routine inventory of our breeding colony in Spring, 1995. There were 554 female monkeys (299 IN, 255 CH) and 279 male monkeys (174 IN, 105 CH). Measurements taken were body weight, body length, head width, head length, and length of the right ulna, tibia and femur. The analysis was done separately for males and females. Age categories were one, two, three, four and five years of age. All adults (5-9 years of age) were included in the "five year" category. An analysis of variance with independent measures was done for each body measurement, by age and by origin. For the males, all measurements increased significantly by age. In addition, CH males were consistently and significantly heavier, had longer and wider heads, and had longer ulna and tibia than IN males. For the females, all measures significantly increased with age except femur length, and weight and tibia length exhibited an interaction effect. CH females were heavier and had longer tibia than IN females while juveniles, but IN females were heavier and had longer tibia than CH females as adults. In this colony, CH rhesus monkeys are larger than IN rhesus monkeys as juveniles, and CH rhesus monkeys exhibit more sexual dimorphism as adults.